The fifth generation (5G) wireless communication concept denoted as New Radio (NR) is a further evolution of the fourth generation (4G) wireless communication concept denoted Long Term Evolution (LTE). LTE and other legacy cellular wireless communication concepts are typically deployed on carrier frequencies below 3 GHz, while NR is designed for use on carrier frequencies up to, and even above, 20 GHz. In NR, carrier frequencies above 6 GHz are mainly intended for hot spot scenarios, while carrier frequencies below 6 GHz are intended also for macro deployment.
NR allows for tight integration with LTE, e.g. considering seamless handover with short interrupt times in the communication. Tight NR-LTE integration provides for the possibility to gradually deploy NR on the same carrier frequencies as LTE. Due to such deployment flexibility, it is will typically be preferable if multi-RAT wireless communication devices (WCD:s; e.g. User Equipments (UE:s)) are capable to simultaneously monitor more than one RAT to provide good mobility performance; both from a system capacity perspective and from a user quality of service (QoS) perspective. For example, a WCD capable of both NR and LTE communication should preferably be able to monitor both NR and LTE in relation to mobility.
The monitoring capability for each RAT may preferably be related to one or more carrier frequency and/or more than one frequency band. Furthermore, capability to simultaneously monitor two or more RAT:s may preferably include a capability to monitor different RAT:s using the same carrier frequency and/or the same frequency band as well as a capability to monitor different RAT:s using different carrier frequencies and/or different frequency bands.
Mobility in LTE typically relies on reception by the WCD of synchronization signals (primary synchronization signal (PSS) and secondary synchronization signal (SSS)) and reference signals (cell specific reference signals (CRS)). The synchronization signals (PSS/SSS) are transmitted by network nodes every 5 ms and the reference signals (CRS) are transmitted by network nodes in every slot. The synchronization signals (PSS/SSS) are typically used for cell detection and identification and the reference signals (CRS) are typically used for signal strength measurements (e.g. reference signal received power (RSRP)). Radio resource management (RRM) measurements are performed using the 6 resource blocks located in the center of the system bandwidth (BW) in LTE.
Mobility in NR typically also relies on reception by the WCD of synchronization signals. However, the synchronization signals may typically be transmitted every 20 ms in NR (PSS/SSS that will be used for cell search will be transmitted every 20 ms; PSS, SSS and PBCH (Physical Broadcast CHannel) will constitute a sync signal (SS) block that will be transmitted in beams in different directions within a 5 ms interval of the 20 ms period). RRM measurements may be performed using mobility pilot signals in NR, which mobility pilot signals may be transmitted with a configurable time interval. The synchronization signals and the mobility pilot signals may not be transmitted in the central part of the system BW for NR. The synchronization signals and the mobility pilot signals in NR may instead be transmitted using absolute frequency values defined in the standard, or may be transmitted using frequency values configured by the serving network node (NWN; e.g. a gNodeB).
Thus, different mobility measurement procedures are needed for NR and LTE in a multi-RAT WCD. To this end, it should be noted that the measurement unit(s) in a WCD typically constitute a finite resource. Hence, the WCD is typically only capable to measure a finite number of RAT(s) per time unit; the measurement in relation to each RAT relating to a number of carrier frequencies, a number of cells, and/or a number of transmission beams.
Due to such (and/or other) circumstances the complexity of RRM measurements may become quite high. In some situations, the complexity of RRM measurements may, for example, implicate requirements that are cumbersome, or even impossible, for the wireless communication device to satisfy.
Therefore, there is a need for approaches to RRM measurement control when NR and LTE are co-existing.
It should be noted that, even though these two RAT(s)—LTE and NR—are used for exemplification herein, similar problems may arise and embodiments may be equally applicable in any scenario where RRM measurements need to be performed for two or more RAT:s.